River herring were so common during colonial times that wagons couldn't cross rivers during spawning runs without crushing them. Today, their numbers are so depleted that an environmental group says they should be protected under the Endangered Species Act.

Saying that river herring populations are a "tiny fraction" of their historic size along the East Coast, the Natural Resources Defense Council filed a petition Aug. 1 asking that they be listed as a threatened species under the act.

Without protection, the two species of river herring - alewife and blueback herring - "are likely to become endangered and eventually extinct throughout all or significant portions of their ranges," the petition stated.

The petition was filed with the National Marine Fisheries Service, a part of the National Oceanic and Atmospheric Administration, which has 90 days to determine whether to conduct a full review of river herring status. If it does, the NMFS would have a year to make a recommendation about whether to list the species.

The petition is the latest salvo in an ongoing battle between conservation groups and management agencies over the fish. Last fall, EarthJustice filed suit against the NMFS and the Atlantic States Marine Fisheries Commission contending they had done too little to protect the river herring. The NMFS is in charge of fisheries in federal waters - those more than three miles offshore - while the ASMFC manages migratory fish in state waters.

Many conservation groups contend that fishery managers do not adequately take into account the importance of river herring and other forage fish, including menhaden, as a food source for other fish when making management decisions.

"I think it ups the ante a little bit," said Bill Goldsborough, senior fisheries scientist with the Chesapeake Bay Foundation. The CBF has not taken a position on the river herring petition, but Goldsborough said the NRDC's petition "has merit and ought to be evaluated thoroughly because they are severely depleted coastwide. They are at an all-time low, and they are a couple of very important forage species."

Peter Baker, director of the Pew Environment Group's Northeast Fisheries Program and the Herring Alliance, a coalition of groups dedicated to restoring ocean ecosystems, said the listing was "strongly warranted."

"River herring are a keystone fish that provide food for many top predators, such as striped bass, ospreys and river otters both at sea and in freshwater," Baker said. "The federal government must take steps to protect these fish in their ocean environment in order to prevent the possibility of their extinction."

Alewife and blueback herring, smaller cousins of the American shad, were once the most numerous anadromous fish to migrate up rivers in the Bay watershed. Spring spawning migrations contained numbers of fish unfathomable today: One account estimated the river herring harvest in just the Potomac River at 750 million fish in 1832. The fish migrate farther upstream, and into smaller creeks, than do the larger American shad.

Their massive spring migrations provided an essential food source for nesting eagles and osprey, as well as for other fish such as striped bass. Native Americans and early colonists relied on those early spring migrations for food after winter, but the fish were so plentiful they even used them for fertilizer.

Adults of both species can reach lengths of around 10 inches and weigh around 8 ounces. While they live most of their lives in the ocean, they return to their native rivers to spawn when they are around 4 years old. Each adult female can produce between 60,000 and 100,000 eggs, but only 1 percent of the eggs will produce a fish that makes it all the way back to the ocean.

The petition recites the litany of factors that led to the decline of the species, starting with large historic fisheries in their spawning rivers; construction of dams that blocked huge areas of historic spawning habitat; and poor water quality in spawning areas. Gradually, spawning populations for some rivers along the coast began to disappear.

In the 1960s, foreign fisheries became established just off the East Coast which, the petition states, "sent populations into a freefall" as they caught huge numbers of herring and other fish until the United States acted years later to force their exit.

River herring populations never rebounded from that hit. In the last decade, their numbers appear to have declined even further. Much of that, according to the petition, stems from "significant mortalities" when river herring are caught as bycatch in fisheries targeting other species in federal waters. In the last decade, ships involved in some of those offshore fisheries have gotten larger, and are towing bigger nets - some five stories high and as wide as a football field, according to the petition.

In the future, the petition stated, climate change will pose a "grave threat" to both species by worsening water quality in spawning areas and altering the flow patterns of rivers. Because river herring are divided among river-specific spawning stocks, the ability of a specific stock to migrate as temperatures warm or conditions worsen is limited.

The petition recounted the significant drops in river herring numbers in rivers along the coast, including those in the Bay.

In Maryland, annual harvests of river herring averaged 3.57 million pounds from 1950 to 1970, but have dropped to an average of only 45,570 pounds per year in recent years, an overall decline of almost 99 percent.

In Virginia, annual harvests which once averaged about 24.92 million pounds dropped to an average of about 85,000 pounds in recent years.

The Potomac River, which an 1896 government report called the "leading alewife stream" in the United States, has seen harvests drop from an annual average of 6.77 million pounds between 1960 and 1970 to an annual average of 7,148 pounds.

The Susquehanna River, where harvests totaled 6.7 million pounds in 1920, has almost nothing today.

River herring fisheries have already been closed in Massachusetts, Rhode Island and Connecticut and many others, including most of those that remain around the Bay, are likely to be closing next year as a result of new requirements from the ASMFC.

At the federal level, the NMFS lists alewife and blueback herring as "species of concern."

But the petition said those actions "are not nearly enough," contending that managers continue to lack coordinated, effective and comprehensive management measures that adequately protect river herring throughout their ranges.

Continued threats, the petition said, are great enough that river herring could become endangered in the foreseeable future — which is the definition of a threatened species under the Endangered Species Act.

If river herring are listed as a threatened species, the petition said a recovery plan should be written that improves their protection from ocean bycatch; improves water quality by reducing nutrients and other pollutants; requires fish passages or dam removals; restricts dredging in spawning areas and during spawning seasons; and designates critical habitat for special protection.

In 2009, the NRDC petitioned to have the Atlantic sturgeon listed as an endangered species. After a review, the NMFS last October also recommended the Atlantic sturgeon be listed as endangered. A final decision is expected this fall.